Arsenal tonight appeared to have ­succeeded in their attempt to sign the midfielder Andrei Arshavin from Zenit St Petersburg when the player's agent ­confirmed a deal had been agreed but that the club must still wait for the Premier League to ratify the ­transfer tomorrow.

"It was completed in extra-time but we must wait for confirmation," said Dennis Lachter. "In 16 years this has been the most difficult transfer ever." The Premier League confirmed that a number of transfers remain to be signed off tomorrow and Arshavin's is understood to be among those.

The 27-year-old's arrival at the Emirates for a fee of about £15m represents a telling departure in Arsène Wenger's player recruitment policy. Arsenal's manager is notoriously sceptical about buying footballers already at their peak and of conducting business in the mid-season window. But with Arsenal five points behind fourth-placed Aston Villa Wenger is under severe pressure to ensure qualification for next season's Champions League. He is thus in need of a proven performer.

The deal is also notable for the unique part played by the fee demanded by Zenit from Arshavin, which was the sticking point throughout the month, and came close to scuppering the move right up to yesterday's 5pm deadline.

The playmaker received a huge signing-on "loyalty bonus" when he re-signed for the Russian club in 2006, which was awarded on the understanding that Arshavin would complete his four-year contract. Having spent a little over two and a half years in St Petersburg the club's board demanded the difference be returned by Arshavin, and it was only in the final minutes, after a fortnight of brinkmanship from the differing parties, that agreement was reached.

The day had begun with Arshavin waking up in a Hertfordshire hotel, after he had flown to the UK to prepare himself for a medical in case of the deal going through. But those hopes appeared to have died at about midday, when Arshavin was reported to have left for a nearby airport after his advisers had decided that Arsenal's salary offer to Arshavin, plus Zenit's demand for the part repayment of the loyalty bonus, were unacceptable.

At that point sources close to the midfielder had said they were furious with both Zenit and Arsenal, claiming the on-off saga was "definitely off. We're very disappointed, a deal has been worked on for nine months. First it was Tottenham last summer, now Arsenal," one source said. "What's the problem with this deal? Money as always. The Russians are animals and how can Arsenal offer less than £15m and half of Arshavin's contract?

"He's getting ¤3.875m and the club is offering half. Who would take another job for half the money? Arsenal have been making big waves by saying this would be the big historic transfer in the history of the Gunners. Well, it's bull. They thought they could pull this off by saying we are a big club, this is a nice country, all that stuff. But he's not a 16-year-old from Africa. The life in England is more expensive – a car, a house, it's all more expensive in London, and he has to bring his family, he has one kid who is three years old, another who is one years old. It's ridiculous."

Executives at the Emirates, who had woken convinced Arshavin was certain to become an Arsenal player, now began frantic work to save the deal. By 5pm Arshavin had passed a medical, a fee between the clubs had been agreed, a settlement reached on Arshavin's contract demands, and the requisite papers were filed with the Premier League. Whether a compromise was found regarding the amount Zenit demanded from Arshavin, and if this was paid by the player or his new employers, is still unclear.

• This article was amended on Tuesday 3 February 2009. Andrei Arshavin actually re-signed for Zenit in 2006, rather than signing for them; he had been in the club's first team since 2000. This has been corrected.